What is the sum of the first (7) terms of the AP (40,35,30,\ldots)?
Answer and explanation
Correct answer: 175
Here, \(a=40\), \(d=-5\), and \(n=7\). The seventh term is \(a_7=40+(7-1)(-5)=10\). Hence, \(S_7=\frac{7}{2}(40+10)=175\). Therefore, 175 is correct. A result such as 180 may arise from an error while adding the terms. Exam tip: check the last term using \(n-1\) before applying the sum formula.
Frequently asked questions
What is the correct answer to this question?
175
Why is this the correct answer?
Here, \(a=40\), \(d=-5\), and \(n=7\). The seventh term is \(a_7=40+(7-1)(-5)=10\). Hence, \(S_7=\frac{7}{2}(40+10)=175\). Therefore, 175 is correct. A result such as 180 may arise from an error while adding the terms. Exam tip: check the last term using \(n-1\) before applying the sum formula.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Arithmetic Progressions (AP). Topic: Finding the sum of the first $n$ terms of an AP.
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